Computer assisted image guided medical and surgical navigation systems are known and used to generate images in order to guide a doctor during a medical procedure. See, for example, U.S. Pat. Nos. 5,769,861 & 6,428,547. Such systems frequently include a tracking array that is clamped to the instrument desired to be tracked.
U.S. Pat. No. 6,190,395 (“Williams”) discloses an IGS system having a flexible clamping band used to attach the tracking array to the instrument.
U.S. Pat. No. 6,021,343 (“Foley '343”) discloses a tool for use in image guided surgery comprising an annular guide member having a trackable array and a drive shaft for rotating an instrument such as a screwdriver while keeping the array stationary. In particular, Foley discloses a trackable medical instrument for use in a computer assisted image guided surgery system having a digitizer for tracking the position of the instrument in three dimensional space and a display providing an indication of the position of the instrument with respect to images of a body part taken preoperatively, the instrument comprising: a) a guide member having a tracking device mounted thereon for being tracked by a digitizer; b) a drive shaft contained within the guide member, the drive shaft having a longitudinal axis and a proximal and a distal end, the drive shaft being rotatable within the guide member while being fixable within the guide member in a direction of the longitudinal axis; c) an instrument tip extending from the proximal end of the drive shaft; wherein the instrument tip rotates freely relative to the guide member while being fixable axially relative to the guide member; and d) a drive handle extending from the distal end of the drive shaft for guiding the instrument, including the guide member, and for imparting rotary motion to the drive shaft and the instrument tip independent of the guide member. In each embodiment disclosed in Foley '343, the drive shaft is received within an annulus of the guide member. That is, the annulus of the guide member surrounds the drive shaft, thereby allowing the array to rotate fully around the drive shaft.
Further, Foley '343 discloses attaching the instrument to the drive shaft by a simple male-female socket, in particular a ball-and-detent mechanism. The ball and detent feature of this socket produces considerable error in tracking because the attachment occurs on one side of the connection and so is not substantially radially uniform.